AMIR ZANDI admits he was a typical teenager when it came to his diet – regular trips to fast-food restaurants and lots of soft drinks.

But when the 17-year-old HSC student from Gordon became so fatigued he could barely drag himself out of bed, was losing concentration in the classroom and sleeping up to 15 hours a night, he knew something was wrong.

Amir was diagnosed with insulin resistance – which reduces uptake of energy-producing glucose in the body – and put on a low GI (glycemic index) diet. The GI is a measure of the effect of sugars and starches on blood glucose levels. He now has a low GI/high carbohydrate breakfast , eating either wholegrain cereals , multigrain breads, natural muesli, baked beans, poached eggs, fruit and plain or diet yoghurt.

Now an increasing body of research linking low GI and academic performance is prompting doctors to urge parents to consider changing their children’s diets.

Alan Barclay, chief scientific officer at the Glycemic Index Foundation, a partnership between the University of Sydney and the Juvenile Diabetes Research Foundation , said parents wanting to improve their childrens’ school performance should give them a breakfast with about 35 to 40 grams of carbohydrate with a low GI.

‘‘ That should translate into improved performance in various tasks at school which ultimately should lead to better marks at the end of the year,’’ Dr Barclay said.

‘‘ Glucose is the primary fuel for our brain. If we don’t have enough in the right amounts over the right period of time we basically can’t think properly and can’t remember things.’’

Research by British academics published in the European Journal of Clinical Nutrition in 2010 found a low GI/high carbohydrate breakfast improved the cognition and attentiveness of children and helped them complete maths tasks more quickly and accurately.

Amir said his his concentration levels had massively improved and he no longer felt tired during the day. He also lost about 15 kilograms in seven months.

‘‘ My parents thought I was just being a lazy teenager, but I was just so, so tired,’’ he said. ‘‘ It was a bit scary actually, not knowing what was wrong with me.’’